Detonation analyzer



June 1, 1954 D. R. DE BOlS BLANC 2,679,746

DETONATION ANALYZ R Flled Oct. :51, 1949 2 Sheets-Sheet 1 [IO DETONATION PICKUP HIGH PASS LOW PASS FILTER FILTER H V THRESHOLD PEAK |,I5I A DEVICE DISCRIMINATOR r 1 5c I/ZB PULSE PULSE I I" SHAPER SHAPER I 2a 30 S29 k3! 27 l TRIGGER cIRcuIT 17k CLIPPING 36 cIRcuIT HQ 2 IO\ DETONATION PULSE PICKUP CONVERTER 1 35 HIGH PASS j FILTER INTERGRATING cIRcuIT I 1 I THRESHOLD IGNITION 3 DEVICE PULSE PICKUP I 7 2| es METER PULSE PULSE 'SHAPER SHAPER TRIGGER F/GJ FIG 4 CIRCUIT INVENTOR. D.R. DE BOISBLANC WMMAZM A TTORNEYS Jun 1, 4 D. R. DE BOISBLANC DETONATION ANALYZER 2 Sheets-Sheet 2 Filed Oct. 31, 1949 Patented June 1, 1954 TENT OFFICE DETQNATION ANALYZER Deslonde R, de Boisblanc, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application October 31, 1949, Serial No. 124,667

6 Claims.

,This invention relates to a detonation analyzer for indicating the instant at which detonation occurs during each operating cycle of a piston in aninternal combustion engine.

When an internal combustion engine is operating normally without the occurrence of any detonation-in the cylinders thereof, the curve rate of change of pressure inthe cylinder to time resembles a single cycle of a damped sinusoidal wave, this wave hereafter being-referred to as the main pressure, wave. vWhen detonation occurs in the cylinder, a high frequency component is superimposedupon the damped sinusoidal wave a short interval after the first. maximum or peak thereof. Detonation meters heretofore utilized in .the prior art separate this high frequency component representative of detonation from the low frequen'cy'sinuosidal component and from other .high frequency ,componentsof the pressure wave, such as those resulting from valve closurebperation of the-injector in certain airplaneengines, and occurrence. of the ignition spark. After amplificatiomthe signal representative. of detonation is measured and its amplitude is.. consider ed to be proportional to the intensity of cletonation.

I have found that ,theineasurement' of detonation intensity. made by thi's method does not, in all cases, give; reliable quantative results. As previously noted, the high frequency detonation component is superimposedv upon the damped sinusoidalmain pressure wave and occurs slightly afterthe first maximum or peak thereof. Accordingly; shifting vof the detonation signal along the, time axis ofthe sinusoidal wave produces an a'pparent'variation in the intensity of detonation since, the amplitude of. the sinusoidal wave :is

continuously. decreasing with time after the maximum value has been reached. That is, a detonatiohcomponent superimposed upon the main pressure wave at a region near its peak will give a substantially higher reading on the detonation meter than a .detonation component of equal intensitysuperimposed upon a declining portion of the sinuosoidal wave where the amplitude of the sinusoidalwave is less than its peak amplitude,

This shifting of the detonation component along the time axis may produce a false reading of detonation. both with electronic detonation meters, such-as those approved'by the ASTM, and in the older-bouncing pin type of measurement.- The shifting may occur as a result of occurrence of detonation'at different regions of the cylinder. It will be apparent that the greater the distance of the region of detonation from; the detonation pickup, the further will the detonation component be displaced along the time axis of the sinusoidal mainv pressure wave. I In accordance with this invention, I produce a timing pulse at a predetermined part of the cycle of the piston in the cylinder at which the detonation measurements are taken, and the time interval between each timing pulse and a pulse representing the instant of detonation is measured to provide a voltage which is proportional to the shift of. the detonation component along the time axis. This voltage may be applied to the output voltageof an electronic detonation meter to provide a correctionfor the shift of the detonation component along-the time axis or, alternatively, the comparison voltage may be utilized to determine whether or not a test engine is in propercondition for determining the detonation characteristics of its fuels.

It is an object of the invention to provide a detonation analyzer for determining the time at which detonation occurs during each operating cycle .of a cylinder under test.

It is a further object to provide an analyzer which is of simple construction, rugged in operation, and utilizes a minimum-number of standard circuit components.

Various other objects, advantages and features of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, in which:

Figure 1 is a block diagram of the detonation analyzer;

.Figure 2 is a series of. graphs illustrating the wave form at various parts of the instrument of t Figure 1; l

Figure 3 is a schematic-circuit diagram of a portion of the circuit of Figure 1; and t Figure 4 is a block diagram of a modification of the invention. A r Referring now to the drawings in detail, and

particularly to Figure l, a detonation pickup. I0.

is mounted upon the cylinder of an internal com-. bustion engine which is to be tested, this pickup operating in a known manner to oonvertp fes-v sure variations in the cylinder into electrical voltages representative thereof. Asshown by Figure 2, the voltage wave produced by the pickup in-- cludes a damped sinusoidal component! representative of the main pressure wave in the cylinder together with high frequency compo nents l2, l3 and i4 representing valve actuation and the ignition spark. When detonation occurs in the cylinder, a high frequency component l5 is superimposed upon pressure wave II. In the example shown, detonation component I5 occurs a short interval after the main pressure wave I I reaches its maximum amplitude at I6. As previously stated, under certain conditions of engine operation, detonation component I5 may shift laterally along the time axis with a resultant change in the length of the interval between peak amplitude I6 of the main pressure wave and detonation component I5. It is this interval which is measured by the apparatus of this invention. As will become apparent from the'following description, the occurrence of the ignition spark, as indicated by high frequency component I3, in some cases, may also be used as a reference for measuring the displacement of detonation component I5 along the time axis under some conditions.

In the circuit of Figure l, the output of the pickup II) is fed to a high pass filter I8 which passes detonation component I5. it will be noted that the wave form at the output of filter I8 includes filtered detonation component I5a and high frequency components I2a, Ba and I la corresponding to the components I2, I3 and I4. It will further be noted that the main pressure wave II, which is of low frequency,

is rejected by filter I8 and does not appear at the output thereof. The output of filter I8 is then fed to a threshold device I9 which passes only components of greater than a predetermined amplitude, as indicated by horizontal line 20, Figure 2. As a result, the output of threshold device I9 consists only ofa high frequency wave I5b representative of the detonation component I5. This pulse is fed from threshold device I9 to a pulse shaper 2I where it is convertedinto a single sharp pulse I5c which, occurs,

during each cycle, at the precise instant of detonation. A suitable detailed circuit corresponding to the elements of the block diagram thus far described is shown in my U; S; Patent 2,448,323; entitled Detonation Meter."

In accordance with the invention, the output of the pickup I is also fed through a low pass filter 22, a peak discriminator 23, and a pulse shaper 24 to produce atiming pulse which occurs at a predetermined part of each operating cycle. In this embodiment of-the inyention, the timing pulse is produced as the main pressure wave I I',. Figure 2, reaches its maximum value. To this end, iow pass filter 22- is selectively tuned to the frequency of main pressure wave II so that the output thereof consists of a damped sinusoidal wave I I a corresponding to the main pressure wave II, the high frequency components I2, I3}

I4, and I beingeli ninated by the action ofithe filter. The peak discriminator. 23, converts wave I Ia into a rectified pulse 'which is .not of suflicient sharpness as to produce an. accuratetiming signal. Thereupon thepulse shaper- 24 converts pulse 25 intoa sharp, timingpulseZG which occurs I at the instant. main pressure wave- II reaches its maximum Value. The individual circuits 0f fi-lter 22,- peakdiscriminator =23and pulse shaper 24. are well knewn,and,- hence, neednot be described in detail herein,- theinvention-resid ing in .the combination of l these circuits to produce new results.

The outputs of pulse shapers 2 I and. '24 are -fed to a, trigger circuit 21; which-maybeoffthe type colloquially referred to aspa flip-flop. circuit..- This-circuit has twostable limiting conditions with an unstable region therebetwenandzthe circuit is changed alternately to its two stable conditions by the successive pulses produced by circuits 2I and 24. In particular, referring to Figure 2, the circuit 21 is stable when the anode circuit of one of its tubes is at the voltage represented by line 28 or at the voltage represented by line 29 while it is unstable at anode voltages represented by the portion =o'f the graph between lines 28 and 29. As a result, the incidence of pulse I50 upon the trigger circuit produces a sudden increase, represented by line 30, in the anode voltage and, thereafter, the incidence of pulse 26 upon thecircuit produces a sudden decrease in anode voltage, as represented by line 3I. It will be apparent, therefore, that the output of trigger circuit 21 is a rectangular wave whose width'W is proportional to the time inter- In Figure 2, v

" is fed by the output of pulse converter 33:

val between pulses I5c and. In the circuit, as described, the interval measured is that between the detonation component I 5- of one cycle of operation and the maximum amplitude I6 of, the pressure wave of the ;next succeeding cycle of operation. By a simple adjustment of the dircuit, the interval between the maximuinainpli tude I6 and the detonation component I5 of the same cycle of engine operation maybe measured.

The rectangular waves produced by trigger circuit 21 are fed to a clipping circuit 32 which passes only voltages between predetermined ain'- plitude limits, thereby to eliminate variations in amplitude of the rectangular waves. The modified rectangular waves from circuit 32 arefed to a pulse converter circuit 33 which produces v a pulse 34 corresponding to each rectangular wave, the height 'H of pulse 34 being' 'propor tional to the width W of the correspondingjred-' tangular wave. This circuit, in ei'fect, amplifie's' the width variations of the rectangular waves and provides a wave form" which is more'r'e'adily acted upon by an integrating circuit 35 which The circuit 35 produces a' voltage Wave 3'6, the aim plitude of which is proportional" to the" average; height H of' pulses 34", and to the average width;

' W of the rectangular waves-'produced'by: tlie'trig-j ger circuit over a number of operating cycles'. Accordingly; the integrated wave' form" 36' has anamplitude proportional" to the average time in terval between" pulses I5c'and' 2- over a number" of operating cycles which; in turn; is pro er-v, tional to the average displacement of d"etoriat-io'ri component I5 along the time axis" from eak?- amplitude I6 of' the wave II. The integratedii output of the circuit 35is'f edto a'me'ter 3If'whicli'j may be-either a conventional milliam'met'er or a vacuumtube=voltmeten As previously mentioned, if detonationcome ponent I5 occurs at the peak portion IQ: of the": main pressurewave; it's apparent-amplitude; greater than if the detonation c'omponentdsf] shifted rightwardly along the time axis so that r. it is superimposed upon a region of the curve I I, such as that indicated' at 3 8i In order" to illustrate this point more clearly, a detonation" v component39jhas been shown sup'erpc'ised' upon the curve II at the"region" 38"thereoff It be evident that the apparent amplitud'iofc' ponent 39 is lessthan" that of component although} infa'ct, both"- components" are'o the same amplitude; Measurement of thetime terval between detonation component I 5 and predetermined region of the" operating' curv such as "peak amplitude I 6," .permit's the effect the shifting of detonation component 1 l 5' 'alo "the time axis to r be" readily com'pen'sated ma Thus, the output of the described analyzer may either be mixed with the output of an electronic detonation meter as a correction voltage, or a test engine may be operated until a stable con-j dition is obtained wherein detonation occurs during or at a predetermined part of each operating cycle. Thereupon, the output of the detonation meter is proportional in a quantitative manner to the intensity of detonation.

The detailed circuit of unit 21 and subsequent;

units is shown by Figure 3, in which the output of pulse shaper 2| is fed to input terminals 40, 4I and the output of pulse shaper 24 is fed to input terminals and 42. Each set of input terminals is shunted by a grid resistor 43 and the respective terminals 4|, 42 are connected to' the control grids of the first stage tubes of two separate audio amplifiers, each amplifier includductor 50 having a grounded by-pass condenser 5| attached thereto. The conductor 56 is supplied with current in the usual manner by a power pack including a power transformer 5|, a dual diode rectifier tube 52, a filter inductance 53, a resistor 54, by-pass condensers 55, 56 and a voltage regulator tube 51. The anodes of dual triode 44 are connected through coupling condensers 58, respectively, to grounded potentiometers 59, the sliders of which are connected to the respective control grids of dual triode 45. The'anodes of dual triode 45, in turn, are connected through coupling condensers 6i], respectively, to the control grids of dual triode 46, each control grid having a grounded gridresistor 6| connected in circuit therewith. Accordingly, the dual triodes 44, 45 and 46 comprise two separate three stage amplifiers, each of which amplifies the output voltage of one of the pulse shapers 2| or 24, the amplifier gain being controlled individually by potentiometers 59.

The anodes of dual triode 46 are connected through coupling condensers 62, respectively, to

the control grids of sections 63, 64 of a dual triode 65, each of said control grids having a grounded grid resistor 65 connected in circuit therewith. Tube 65 and its associated components constitute the trigger circuit 2'? of Figure 1. The anodes of dual triode 65 are connected to positive power supply conductor 50 through the respective decoupling resistors 67, and the anode of triode section 63 is connected to the control grid of triode section 54 by a resistor 63, while the anode of triode section 64 is connected to the control grid of triode section 63 by a resistor 69. The cathodes of the dual triode 65 are interconnected and are supplied with operating potential from a voltage divider 16.

Due tothe cross connection of the control grids and anodes of triode sections 63, 64 by resistors 68 and 69, the circuit has two stable limiting conditions with a region of unstability therebetween. In one stable condition, tube 63 is conductive while tube 64 is non-conductive and in the other stable condition tube 64 is conductive while tube 63 is non-conductive, the circuit being changedv from one stable position to another by application of a negative voltage pulse to the control grid'of the conductive tube. Assuming that tube 64 is non-conductive and tube 63 is conductive, application of a detonation pulse to termurals 46,4! from pulse shaper 2| causes tube 63 to become non-conductive with the result that the anode voltage of tube 63 rises suddenly and tube 64 becomes conductive due to the resultant increase in its control grid voltage. Thereupon, application of a timing pulse to terminals 40, 42 from pulse shaper 24 causes tube 64 to become non-conductive with the result that tube 63 becomes conductive and its anode po tential' decreases abruptly to its original value. Thus, arectangular wave is produced at the anode of tube 63 whose width is proportional to the time interval between the detonation pulse and the timing pulse, as set forth in connection with the description of the block diagram, Fig ure 1.

The rectangular waves from trigger circuit 21' are then passed through a condenser 12 and a resistor 13 to clipping circuit 32 which consistsoif a diode 14 having its anode grounded and its cathode connected to the adjacent terminal of resistor ,13 together with a diode 15 having its anode connected to the adjacent terminal of resistor 13 and its cathode connected to a volt-' age divider network including a variable resistor 16, and fixed resistors 11 and 13, resistor 18 be" ing shunted by a by-pass condenser 19. Diode 14 by-passes to ground components having less than a predetermined voltage while diode 15 Icy-passes components having a voltage greater than a predetermined maximum value. Accordingly, the clipping circuit 32 confines the amplitude' of rectangular waves 29, Figure 2, within 4 predetermined amplitude limits.

The output of clipping circuit 32 is fed to the control grid of a triode 86 having its anode connected to conductor 50 and its cathode connected to ground through a resistor 6|. The output from the cathode of this tube is fed to pulse con verter circuit 33 through a resistor 82 which is connected to the control grid of a triode 84 and to ground through a condenser 85. When a rectangular wave is fed to condenser 85, the condenser charges in an exponential manner to produce a voltage pulse whose amplitude is proportional to the width of the rectangular wave fed thereto, the resultant pulse of variable amplitude being fed to tube 84 which has its anode connected to lead 56 and its cathode connected to an integrating circuit comprising accumulating condensers 86, 61 and resistances 88, 89, these com-'- ponents making up the integrating circuit 35 of Figure 1. is a voltage wave whose amplitude is proportional to the amplitude of the pulses fed thereto by having its anode connected to conductor 50, and having its cathode connected to ground through a resistor 92. The meter has one terminal thereof connected to a voltage divider network formed by a variable resistor 93 and a fixed reistor 94, while the other terminal is connected through a resistor 95 to the cathode of tube 9|. Accordingly, the meter 96 reads theintegrated.

- output voltage produced by the circuit 35.

In Figure 4, I have shown a modification "oi The output of the integrating circuit- I-Ience, the integrated voltage is also.

a ses-46 the circuit-of this invention wherein the-timing pulse is derivedfrom theignitionsystem, rather than from a peak discriminator responsive to the peak value of the main pressure-wave. This circuit includes a detonation pickup I9, high pass filter 18, threshold device l3, pulse shaper 21, and trigger circuit 21 similar to those already described in connection with Figures 1, 2 and 3. In this circuit, the filter 22, peak discriminator 23, and pulse shaper Mare replaced by anig nition pulse pickup 9'! which produces a voltage pulse at the instant ignition occurs in the cylinder under test. A suitable circuit for producing such a pulse is shown inU. 3 Patent 2,291,04l5 to J. H. Lancor, Jr., entitled Synchronizing Arrangement for Detonation Detectors. The pulses produced by pickuptl are fed. to a pulse shaper 98 which produces a sharp timing pulse at the instant of ignition, this timing p'uls'e being fed to the trigger circuit 21 in the manner described in connection with Figure 1, suchas by connecting the pulse shaper output to the terminals 40, 42 of Figure 3. In this case, the output of the analyzer is proportional to the average time interval between ignition and the occurrence of detonation'over a number of operating cycles. The use of the ignition impulse as a time reference for the measurement of the detonation interval is very satisfactory since-ignition always occurs at a predetermined part of the operating cycle. Hence, it will be apparent that the output of the circuit of Figure-4c may be utilized to determine when a test engine is in proper condition for the rating of fuels.- 7 While the invention has been described in connection with a present, preferred embodiment thereof, it is to be understood that this description illustrative only and is not intended to limit the invention, the scope of which is defined by the appended claims.

' Having described my invention, I claim:

=1. A detonation analyzer comprising, in combination, a pickup for converting pressure variations in a cylinder of an internal combustion engine into electrical voltages representative thereof, means fed by said pickup for producing asharp pulse of electric current at the instant of detonation, a circuit for producing a sharp timing pulse at a predetermined time during each cycle of the piston in said cylinder, a trigger circuit having two stable positions, means for feeding the detonation pulses to said trigger circuit so that each pulse initiates a rectangular wave in the trigger circuit, means for feeding said timing pulses to said trigger circuit to terminate each rectangular wave, a clipping circuit fed by said trigger circultto limit the amplitude of said rectangular waves within predetermined limits, an integrating circuit fed by. said clipping circuit to provide a voltage representative of the average width of said pulses over a number of operating cycles, and a meter fed by .said integrating circuit.

2. A detonation analyser comprising, in combination, a pickup for converting pressure variations in a cylinder of an internalv combustion engine into: electrical voltages representative thereof, means'fed by said pickup for producing a sharp pulse of electric current at the instant of'detonation, a circuit for producing a sharp timing pulse at a predetermined timeduring each cycle of the piston in saidcylinder, a trigger circuit having-two stable positions, means for feeding the detonation pulses to "said :trigger circuit so that each pulseinitiates a rectangular wave 81 in the trigger circuit, means for feeding said, timing pulses to said trigger circuit to terminate each rectangular wave, a clipping circuit fed by;

said trigger circuit to limit the amplitude of said rectangular waves within predetermined limits, a pulse converter unit for transforming said rec tangular pulses into pulses whose amplitude is proportional to the width of the rectangular pulse, an intergrating circuit for producing a voltage representative of the average amplitudeof the converted pulses and the averagewidth of the rectangular waves over a number of operating cycles, and a meter fed by said integrating circuit;

3. In a detonation analyzer, in combination,.a pickup for converting pressure variations, in a v cylinder of an internal combustion engine into electricalIvoltages representative thereof, afilter selectively tuned to voltage components repre: sentative of detonation, a threshold device fed by said filter for eliminating components of less than a predetermined magnitude, said threshold device producing a sharp voltagepulse eachtime' detonation occurs in said cylinder, means for transmitting a voltage from the ignition system of said engine whichis representative of spark ignition in said cylinder, said voltage therebyl producing a sharp timing pulse at a predetera mined period in the cycle of the piston in said, cylinder, a trigger circuit-having two stablepositions, means for feeding the detonation pulses to said triggercircuit so that each pulse initiates a rectangular wave in the trigger circuit, means for, :feeding said timing pulses to said trigger circuit to terminate. each rectangular wave, a clipping circuit fed by said trigger circuit to limit the amplitude of said rectangular waves within pre: determined limits, a pulse converter. circuit for transforming said rectangular pulses into pulses. whose amplitude is proportional to the width of h the rectangular pulse, an integrating circuit for producing a voltage representative of the average amplitude of the converted pulses and the average .width of, the rectangular waves over a number of operating cycles, and a meter fed by said. integrating circuit. l I

4. In. a detonation analyzer,in combination, a pickup for converting pressure variations in a cylinder of an internal combustion engine into electrical. voltages representative thereof, said voltages including components representative of detonation and a component representative of the main pressure wave in said cylinder, a filter fed by said pickup and selectively tuned to the components representative of detonation, a threshold device fed by said filter for eliminating components of less than a predetermined amplitude whereby said threshold device produces-a sharp pulse each time detonation occurs in said cylinder, a second filter fed by said pickup and selectively tuned to the frequency of said main pressure wave, a peak discriminator circuit fed by said second filter to produce a pulse when said main pressure wave reaches a maximum amplitude,'means for sharpening the pulses produced by said discriminator circuit, thereby to produce a timing pulse during each cycle of the piston in voltages including components representative of detonation and a component representative of the main pressure wave in said cylinder, a filter fed by said pickup and selectively tuned to the components representative of detonation, a threshold device by said filter for eliminating components of less than a predetermined amplitude, whereby said threshold device produces a sharp pulse each time detonation occurs in said cylinder, a second filter fed by said pickup and selectively tuned to the frequency of said main pressure Wave, a peak discriminator circuit fed by said second filter to produce a pulse when said main pressure wave reaches a maximum amplitude, means for sharpening the pulses produced by said discriminator circuit, thereby to produce a timing pulse during each cycle of the piston in said cylinder when the main pressure waves reaches its maximum amplitude, a trigger circuit having two stable positions, means for feeding the detonation pulses to said trigger circuit so that each pulse initiates a rectangular wave in the trigger circuit, means for feeding said timing pulses to said trigger circuit to terminate each rectangular Wave, and means for measuring the average Width of said rectangular waves over a number of operating cycles.

6. In a detonation analyzer, in combination, a pickup for converting pressure variations in a cylinder of an internal combustion engine into electrical voltages representative thereof, said voltages including components representative of detonation and a component representative of the main pressure wave in said cylinder, a filter fed by said pickup and selectively tuned to the components representative of detonation, a threshold device fed by said filter for eliminating components of less than a predetermined amplitude whereby said threshold device produces a 19 sharp pulse each time detonation occurs in said cylinder, a second filter fed by said pickup and selectively tuned to the frequency of said main pressure Wave, a peak discriminator circuit fed by said second filter to produce a pulse when said main pressure wave reaches a maximum amplitude, means for sharpening the pulses produced by said discriminator circuit, thereby to produce a timing pulse during each cycle of the piston in said cylinder when the main pressure wave reaches its maximum amplitude, a trigger circuit having two stable positions, means for feeding the detonation pulses to said trigger circuit so that each pulse initiates a rectangular wave in the trigger circuit, means for feeding said timing pulses to said trigger circuit to terminate each rectangular wave, a clipping circuit fed by said trigger circuit to limit the amplitude of said rectangular waves within predetermined limits, a pulse converter circuit for transforming said rectangular pulses into pulses Whose amplitude is proportional to the width of the rectangular pulse, an integrating circuit for producing a voltage representative of the average amplitude of the converted pulses and the average Width of the rectangular Waves over a number of operating cycles, and a meter fed by said. integrating circuit.

References Qited in the file of this patent UNITED STATES PATENTS Number Name Date 2,225,381 Van Dijck Dec. 17, 1940 2,291,045 Lancor July 28, 1942 2,370,692 Shepherd Mar. 6, 1945 2,448,323 DeBoisblanc Aug. 31, 1948 2,485,584 Ginzton Oct. 25, 1949 2,518,427 Lindberg et al. Aug. 8, 1950 

